AT&T’s board of directors today authorized a share buyback of up to 300 million additional shares.

The amount of shares represents about 5% of its outstanding stock and would be worth some $11.1 billion according to Friday’s closing price.

“This action allows us to continue returning cash to our shareholders through dividends and buybacks while maintaining a strong balance sheet and investing in the future of our business,” said Randall Stephenson, AT&T’s chairman and chief executive.

The move follows a December 2010 authorization under which the company repurchased 143.5 million shares for about $4.6 billion. Including dividends, it now claims to have returned almost $10 billion to shareholders in the first half of 2012.

AT&T has continued to perform strongly, despite the turbulent economy, last week reporting an 8.7% increase in second-quarter net income. The company said its results were helped by an increase in average revenue per mobile subscriber, as customers switch to pricier smartphones and data-usage plans.